Plasma processing of a substrate (for example, etching, film forming process, etc.) has been widely applied in semiconductor manufacturing processes and Liquid Crystal Display (LCD) substrate manufacturing processes. Plasma processing apparatus used for such plasma processing includes an upper electrode and a lower electrode disposed parallel to each other in a processing chamber, allows a substrate, for example, a semiconductor wafer (hereinafter simply referred to as a “wafer”), to be mounted on the lower electrode, generates the plasma of processing gas by applying high-frequency power between the upper and lower electrodes, and etches a film using, for example, a patterned mask.
In such plasma etching, the detection of the end point of the processing using optical data that is obtained at the time of performing the plasma etching is known. For example, it is widely known that a light-emitting spectrum of gas generated by etching is detected as optical data, and the time at which a specific wavelength has been changed is detected as the end point of the etching. Furthermore, a method in which, when light having a specific wavelength is irradiated onto a substrate, the interference light (interference waves) of lights reflected from the boundary surface between a film to be etched and a mask, and from the surface of the mask, is detected as optical data. The etching rate or the film thickness is calculated based on the interference light, and the time at which the desired etching rate or the desired film thickness is achieved is detected as the end point of etching (for examples, see Patent Documents 1 and 2). Patent Document 2 discloses a scheme of calculating an etching rate in a mask having high light transmittance by irradiating two types of light having different wavelengths onto a wafer from a light source in consideration of the light transmittance of the mask.
(Patent Document 1)    Japanese Unexamined Patent Publication No. 2001-217227
(Patent Document 2)    Japanese Unexamined Patent Publication No. 2004-363367
Meanwhile, as semiconductor devices have become diversified recently, the case where plasma processing is performed on wafers having, for example, different types of mask patterns (having different aperture ratios) disposed in the same processing chamber is arising more frequently.
However, in the prior art, in the case where plasma processing was performed on such wafers, the end point of the plasma processing was detected without considering the type of mask pattern, so that experiments carried out by the inventor of the present invention, etc. revealed that erroneous detection of the end point occurred according to the type of mask pattern, even though the material of the mask was the same, with the result that the end point could not be detected accurately. That is, when the type of mask pattern is varied, the characteristics of optical data obtained in the plasma processing vary. Therefore, it could be seen that, when the end point of the plasma processing is detected based on such optical data, erroneous detection of the end point occurs according to the type of mask pattern, and the end point cannot be detected accurately.
In this case, although it is possible for an operator to change the end point detection method of the plasma processing apparatus for each wafer having a different type of mask pattern, that is, for each type of wafer, and then to perform processing, it takes a lot of time to check the type of wafer whenever wafer processing is performed and change the end point detection method each time, and thus throughput is decreased. This problem is not necessarily limited to the case where the type of mask pattern varies, but also occurs in the case where, for example, the type of material of a mask or the type of quality of a film varies.